New topoisomerase inhibitors as proapoptotic agents

DNA topoisomerases (topos) are nuclear enzymes that control the topological state of DNA, carrying out a series of DNA cleavage and religation reactions. Two major forms of topoisomerases are known, topo I and topo II. It is well known that compounds which interfere with topoisomerase activity are highly cytotoxic: the inhibition of these enzymes trigger a chain of events causing cell death. Topo inhibitors, in fact, are among the most efficient inducers of apoptosis. A number of drugs have been identified as dual topos inhibitors and they have shown to have advantages over single enzyme inhibitors, including sensitivity in resistant cells and a broader spectrum of activity. For these reasons outstanding attention is devoted to this class of compounds, not only to find more efficient anticancer agents, but also to find compounds useful to better elucidate the mechanisms on which topos activity is based. On these basis, we synthesized and evaluated a series of pyrroloquinolinones functionalized with dimethylaminoalkyl chains. We obtained a small library of compounds using both conventional synthetic methodologies and microwave assisted organic synthesis, which allowed to prepare derivatives differing in the aminoalkyl chain lenght. For all the compounds the ability to inhibit the cell growth was tested in human tumor cell lines cultured in vitro to perform a preliminary screening. Than, the ability of the compounds to exert their activity through DNA interactions was investigated and the study of the molecular consequences on DNA was completed by evaluating the effects on the enzymatic activity of topo I and II. At the same time, the effect of the tested compounds on the main parameters of mitochondrial functions was evaluated, since it was demonstrated that mitochondria and in particular the mitochondrial permeability transition (MPT) plays an essential role in the cellular apoptosis. So on isolated rat mitochondria the effect of the compounds on membrane potential and mitochondrial swelling was studied, also determining the redox state of the thiols groups and glutathione to establish if the permeability transition could be the result of an oxidative stress. Preliminary results showed that all the derivatives are topo II inhibitors and some of them could amplified MPT, depending upon the chain length, and they could be considered intrinsic apoptosis inducers with potential antiproliferative activity.